All you need to remember is equal parts milk and cornsyrup. I start with about 3 cups of powdered sugar and add milk until there is no "dry" sugar anymore. It is almost more dough-like than anything. Then I add the same amount of cornsyrup that I used for the milk. Add about 5 drops of brite white food color for every cup of powdered sugar. This is a bit thick for flooding, but it works great. I add a bit more sugar to thicken it for outlining when I don't want it to spread at all. If the outlining is just for interest and can spread a bit, I use it as is.

I froze cookies with Toba's glace for about a week. They were double-bagged in freezer bags. I didn't take them out of the bags until they had defrosted, so no condensation had a chance to form on them, which probably would have mucked up the glace.